This invention relates generally to gas turbine engines, and more particularly, to a gas turbine engine stator vane that includes an integral light probe for measuring operating characteristics of rotor blades.
Gas turbine engines typically include high and low pressure compressors, a combustor, and at least one turbine. The compressors compress air which is mixed with fuel and channeled to the combustor. The mixture is then ignited for generating hot combustion gases, and the combustion gases are channeled to the turbine which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
When gas turbine engines operate in various conditions, foreign objects may be ingested into the engine. More specifically, various types of foreign objects may be entrained in the inlet of the gas turbine engine, ranging from large birds, such as sea gulls, to hailstones, sand, and rain. The foreign objects may impact a rotor blade resulting in a portion being liberated from the rotor blade. Such a condition, known as foreign object damage, may cause relatively sharp notches to be formed in the leading edges of the rotor blade. These sharp notches in effect are stress concentrations which may reduce the fatigue capability of the rotor blade. If this condition is not resolved, a portion of the airfoil, usually the tip, may be liberated, thus changing the frequency of the airfoil. When this occurs there will be a flow disturbance around the blade with the missing tip or tip corner. This disturbance can cause a driving force which will drive adjacent airfoils to possible failure.
To measure a frequency change in the rotor blade, a strain gage may be utilized. However, strain gages may not have the desired precision to measure a relatively small change in the rotor blade frequency. Additionally, a light probe may be utilized to measure the change in rotor blade frequency. More specifically, at least one known gas turbine engine includes a threaded opening that is defined through the gas turbine engine casing. The known light probe is inserted through the casing opening to illuminate the rotor blade. However, during operation, the rotor blade tends to centrifuge dirt and/or debris radially outward towards the light probe. As a result, the dirt or debris may accumulate on the light probe thereby lowering the effectiveness of the light probe to accurately measure the frequency of the rotor blades.